Telephone system



Dec. 9, 1958 c, LOMAX 2,863,949

TELEPHONE SYSTEM Original Filed Sept. 13, 1952 9 Sheets- Sheet 1 INVENTOR. CLARENCE E. LOMAX BY I AT TY.

LINE EQUIPMENT I65 Dec. 9; 1958 c. E. LOMAX 2,863,949

TELEPHONE SYSTEM Original Filed Sept. 13, 1952 QSheets-Sheet C590 LINE FINDER LF CIBO 325- LL. m no 5 QRQP GROUP 5 z cnwp 387 FIG. 3 LINK clRcurr IN VEN TOR.

CLARENCE E. LOMAX BY & C &

ATTY.

Dec. 9, 1958 c. E. LOMAX TELEPHONE SYSTEM 9 Sheets-Sheet 4 Original Filed Sept. 13, 1952 C590\ Cl80\ ALARM 129 F|G.4 LINK CIRCUIT INVENTOR. CLARENCE E. LOMAX BY if 6? Z ATTY.

Dec. 1958 c. E. LOMAX TELEPHONE SYSTEM 9 Sheets-Sheet 6 LO M X ATTY.

IN V EN TOR. CIARENCE Original Filed Sept. 13;, 1952 E m a mic. J :05 M m Q o 0 E 25 13 5 M. r: r z o mfiw T h u l .l 2m 8. 51.5 \A3 56 5.525% m 0E Em N8 l; 3 Ll fl $8 if c. E. LoMAx 2,53,949

TELEPHONE SYSTEM Original Filed Sept. 13, 1952 v 9 Sheets-Sheet 7 F|G.7 CODE CALL a CONFERENCE uwn' CB/ MOT. st J rename- 786 CODE CALL 8. CONFERENCE FINDER GE 4" GROUP 3 GROUP 2" GROUP I GROUP I F r 503000 OOOOBOOOQOOOCOO 9200} OOEOEOUQQOOO 000000 000 O 0 050 0 0000 000 00%(0000 006000 ooocououooo 6 000ooufi66906fi00000 ooA OoQo cor- 00cc 00009000000 INVENTOR. CLARENCE E. LOMAX ATTY.

Dec. 9, 1958 c. E. LOMAX 3, 4

, TELEPHONE SYSTEM Original Filed Sept. 13, 1952 9 Sheets-Sheet 8 FIG. 8 832 CODE CALL & CONFERENCE UNIT IN VEN TOR. CLARENCE E. L 0 MAX limited States Patent TELEPHONE SYSTEM Clarence E. Lomax, Hastings, Nehru, assignor to General Telephone Laboratories, Incorporated, Chicago, Ill, a corporation of Delaware Original application September 13, 1952, Serial No. 309,476. Divided and this application May 28, 1957, Serial No. 662,092

Claims. (Cl. 179-18) The present invention relates in general to automatic or semi-automatic telephone systems and more particularly toprivate automatic telephone exchanges. This application is a division of the copending application of Clarence E. Lomax, Serial No. 309,476, filed September 13, 1952, nOW Patent No. 2,824,909.

The principal object of the invention resides in the provision of a simple connector comprising two component switches, especially for use in private automatic exchanges in which special services of one kind or another are provided.

With this object in mind the main feature of the invention resides in'the provision of a connector having .two component switches set by numerical impulses, the wipers of one switch being reached over' the wipers and contacts of the other switch. Both of these switches may be single motion switches in which case one switch may serve as a tens switch and the other as a units switch. The tens switch may have some or all of the following functions: connect the calling side of the connector with the wipers of the units switch either with or without line reversal, thereby to provide for party selection; select a given set of wipers of the units switch; set the units switch on one of a number of start positions preceding a desired one or desired ones of a number of groups of subscribers lines connected to the bank contacts of the units switch; provide for direct access, to the exclusion of the units switch, to a trunk line such as a special service calling trunk or a code call answering trunk or both.

In this manner the connector switch to which the subscribers lines are connected may be of simple construc tion and relatively small capacity and the number of relays associated with each connector maybe limited. Thus a plurality of special services may be provided without unduly increasing the cost of the connector circuits.

In the embodiment of the invention shown herein the invention is illustrated in connection with a private automatic exchange including a special service apparatus which is used in common for both code calls and conference calls, the features relating to this aspect of the subject matter being claimed in the parent application Serial No. 309,476.

More particularly the registering or selecting means which are provided in the code call apparatus to record the identity of the party to be code-called also serve as a means to make the equipment used in setting up a conference effective if this latter service rather than code call service is desired by the calling party.

A plurality of sets of group conference relays are provided, each set of these relays functioning when selected to set up a conference between a fixed group of subscribers. In this case the aforementioned code call registering means may be utilized, to select the particular relay set, that is the particular conference group, desired in a given conference call. In this manner only a single set of bank contacts in the connectors is required to provide a calling connection to the special service apparatus, in spite of the fact that not only code calls but also conference calls to any desired one of a number of groups may be set up over this calling number. This is of particular advantage in private automatic exchanges of relatively small capacity in which only a limited number of contact positions are available in the connectors.

In private automatic exchanges with code call facilities it is customary to provide, in addition to the code call calling connection a code call answering connection to the code call apparatus, together with a talking path interconnecting these two connections. Thus, when the party desired in a code call upon hearing his characteristic code dials the answering number from the nearest telephone he may enter into conversation with the party that originated the code call. At least a part of this code call talking path, preferably including the calling bridge associated therewith, is utilized in the case of conference calls to connect the conference originating party with the con ference talking path set up by the conference equipment. In this manner the party originating the conference call, for example the secretary of an executive may converse with the parties of the conference group called'although she herself is not a member of this group, provided only that she is not restricted from access to the special service apparatus.

Moreover, in the system described herein means are provided for actuating the code call sender associated with the special service apparatus to transmit a special code alarm; this special code alarm overrides a regular code call but does not interfere with conference calls, that is a code alarm may be initiated and transmitted while a conference is in progress.

The invention both as to its organization and method of operation, together with other objects and features thereof, will best be understood by reference to the fol- 1 lowing specification taken in connection with the accom- 1 gang relays and the conference relays individuallyassociated with three of the subscribers lines shown in Fig. 1;

Figs. 3, 4 and 5 when taken together represent a circuit diagram of a line finder-connector link of the aforementioned private automatic exchange;

Fig. 6 is a circuit diagram of the distributor associated with the finder-connector links of this exchange;

Figs. 7 and 8 when taken together form a circuit diagram of a combined code call and conference apparatus associated with the aforementioned private automatic exchange;

Fig. 9 is a circuit diagram of a code call sender associated with the apparatus illustrated in Figs. 7 and 8; and

Fig. 10 illustrates how Figs. 1-9 should be placed relatively to each other in order to show a unified system.

A brief description of the embodiment of the invention as illustrated in the drawings will first be given. The private automatic exchange shown herein relies for the establishment of telephone connections between the sub scribers connected thereto on a number of finder-connector links such as that represented in Figs. 3-5, these links being served by the distributor circuit illustrated in Fig. 6. The capacity of this automatic exchange is assumed to be forty subscrib rs lines which any 1 9 ..,aea,949

individual lines or two-party lines of the side-of-line signaling type, the four lines shown in Fig. 1 being all party lines. As shown in Figs. 1, 3 and 5 these four lines are connected, by way of talking conductors 172, I73; 182, N3; 192, 193; and 136, 146, respectively, to the finder banks over cable C170 and to the connector hanks o er Conductors E75, 185, 195 and 156 are the control conductors connecting the respective line equipments with the finder banks, and conductors 17d. 186, 1196 and 166 are the control conductors connecting the respective line equipments with the connector banks.

Upon the initiation of a call at a subscribers station, say station D, Fig. l, the combined line and cutoff relay, in the instant example 160, Fig. 1, which is of the 2step type. partially operates to close a starting circuit to the distributor, Fig. 6, which is of the link-preselecting type. The distributor switch, DS, shown in the upper portion of Fig. 6 is a rotary stepping switch having any convenient number of positions as required by the number of links served by the distributor. Assuming that the wipers of distributor switch. DS, rest on a set of contacts associated with an idle finder-connector link such as that shown in Figs. 3-5, the line finder, Fig. 3, of that link which is assumed to be a til-position single motion stepping switch will be caused to search for the calling line. if this line is found, the line cut-off relay operates fully to disconnect itself from the talking conductors and open the aforementioned start circuit, the line finder switches the calling party through to the impulse relay, 33b, of the iindenconnector link and the distributor switch advances its wipers to a set of contacts associated with an idle link in preparation for another call.

The connector used in each of the link circuits includes two component switches, one switch, TS, Fig. 5, serving as a tens switch and the other, US, Fig. 5, as a units switch. it may be mentioned at this point that the distributor switch, Fig. 6, the line finder switch, Fig. 3, the tens and units switches, Fig. 5, and the stepping switches shown in Figs. 8 and 9 are all single motion stepping switches of the type in which the wipers are advanced upon the deenergization of the stepping magnet.

Units switch US. Fig. 5. is a 26-position switch with two sets of wipers and contact rows; each of these two sets of contact rows accommodates two groups of ten subscriber lines respectively connected to positions 1-10 and l2-2l of the switch. The normal or home position, 26. of the switch serves as a start position for one of the groups and position ll for the other. It will be clear therefore that if the switch is in its home position its wipers may be advanced upon receipt of the units digit to any of the subscribers lines connected to positions l-l(1 and if the switch is in position 11 its wipers may be set by such impulses on any of the subscribers lines connected to positions 12-21.

The particular group of subscribers lines desired in a given call is determined by the setting of the tens switch TS. that is according to the setting of the tens switch in response to the tens digit dialled this switch connects the calling side of the connector circuit over its wipers and bank contacts with one or the other of the two wiper sets of the units switch; and if the call is to a subscribers line connected to one of positions 12-21 of the units switch it also causes this last mentioned switch to be automatically advanced to start position 11 in the interval between the tens and the units digits. In addition, tens switch TS is arranged for purposes of party selection to determine the side-of-line over which the ringing current is projected.

Thus referring to Fig. 5, if switch TS has been positioned on its position 2, in accordance with a tens digit 2, it connects the calling side of the connector circuit with the upper set of wipers of the units switch in a straightforward way so that ringing current which if the called line has been found idle is invariably applied to the ...1 v ttrdtt Iii) negative wiper of the tens switch is projected over the negative wiper of the units switch and from there to the negative side of the called party line; and since with the tens switch in position 2 the automatic stepping circuit referred to above is not made effective, the units digit subsequently dialled into the connector will set the units switch on a line in the first tens group as indicated in Fig. 5. If this units digit for example is i, it will readily be seen that station A, Fig. l which has the call number 21 and whose ringer is connected to the negative side of the line will be signaled. If switch TS has been set on its position 3 the same group of tens lines is selected but since the upper wipers of the units switch are connected to this position 3 of the units switch in a reverse way, ringing current will be projected over the positive side of the called line and, assuming that the same units digit 1 is dialled as before, the other party A, Fig. l, on the called party line will be rung since the ringer of this station having the call number 31 is connected to the positive side of the line.

if the tens digit has been 4 and the tens switch accordingly positioned on its fourth position the lower wiper set of the units switch is connected up in a straightforward way and, since the automatic stepping circuit for the units switch is not closed in this position, the units digit, for instance 2, will set the units switch on the corresponding line of the second tens group, this group being connected to contacts 1-10 in the lower bank of the units switch as shown in Fig. 5. Station B, Fig. l, which has the directory number 42 and whose ringer is connected to the negative side of the line will accordingly be rung. If on the other hand switch TS has been positioned on its position 5 the same group of subscribers lines will be reached but because of the line reversal provided in this position ringing current will be trans mitted over the other side of the line. Thus if the units digit again is 2, station B, Fig. l, with the directory number 52 will be signaled.

Assuming now that the tens switch has been set on position 6 the upper set of wipers of the ringing switch will be connected up without line reversal as described above for position 2. but in the present instance a circuit is closed for relay 520, Fig. 5, which closes an automatic stepping circuit for magnet 550 of the units switch. The aforementioned circuit which extends over the li .viper and the strapping between contacts 6-9 of the associated contact row of switch TS and over the C3 bank and wiper of switch US to relay 520 is maintained, due to a corresponding strapping of the C3 bank of the units switch. until this switch has reached start position I l in which it is arrested. As a result the wipers of the switch will be advanced in response to the units digit from this start position to one of positions l2-2l and accordingly it line connected to the third tens group selected. Assuming by way of example that the units digit 5 it will be clear from the drawings that station C, Fig. 1. is signaled in this case. With tens switch TS positioned on position 7 a line in the same tens group will be reached but ringing current projected over the positive side of the line. Thus it the units digit dialled again is 5 the ringer at station C, Fig. 5v will be sounded.

if the tens digit is f) or 9 the lower wiper set of the units switch is selected and again the switch automatically dvanced to start position ll so that a line in the fourth tens group is reached; the difference between tens digits 8 and 9 being that with the tens switch in position ringing current is projected over the negative side of the line and with the tens switch in position 9 ringing current goes out on the positive side of the line. Thus if a allin," subscriber, say at station A, Fig. l, dials 8.), station D will be rung since the ringer at this station is connected to the negative side of the line; and if he dials 90 instead. station D will be signalled because at this telephone station the ringer is connected to the positive side of the line.

it will be understood from the foregoingremarlrs that all regular subscribers have two-digit numbers, the first digit ranging in value from 2 to 9. More particularly if the tens digit is 2, 3, 6 or 7 the upper wiper set of the units switch will be selected and if the tens digit is 4, 5, 8 or 9 the lower wiper set will be connected up; if the tens digit is 2, 3, 4, or 5 the units switch will not be moved out of its home position in the inter-digital interval but if the tens digit is 6, 7, 8 or 9 the units switch upon completion of the tens digit will be automatically stepped to its position 11; and if the tens digit is 2, 4, 6 or 8 ringing current will be sent over the negative side of the called subscribers line but if it is 3, 5, 7 or 9, the ringing current will be transmitted over the positive side of the called line.

In each of the instances discussed above it was assumed that the called line was tested free by the connector. on the other hand the called line is busy, busy relay 4-29, Fig. 4, will be operated and busy tone returned to the calling subscriber. Provisions are made in the embodiment described herein for permitting stations especially privileged to these services, for instance executives of a business establishment, to override this busy condition and thereby gain connection to the line called. Subscribers that are given such executive right-of-way privileges have the associated bank contact in the 4th or EC-contact row of the line finders wired to a nonlocking key or push button at their telephone, such a push button designated by reference numeral 17% being schematically shown as provided at station A in Fig. 1. If the executive at this station upon hearing the busy tone depresses this button, relays Mil and 43d, Fig. 4-, operate the finderconnector link to cut this subscriber through to the called line even though this last mentioned line is busy in an outgoing or incoming call.

Reference now is made to Figs. 7 and 8 in which there is shown a special service unit that enables the subscribers entitled to these services to set up either a code call, namely with the aid of the code call sender, Fig. 9, or set up a conference call to a desired one of a number of fixed conference groups, these last mentioned groups being determined by the contact wiring of gang relays such as 27th and 275, Fig. 2. To reach this special service unit the calling subscriber should dial 1 as the first digit. If tens switch TS, Fig. 5, of an idle finder-connector link has been set on its first position in response to the dialing of this digit code call relay 350, Fig. 3, will be operated over the B wiper of this switch and the connector caused to test the busy condition of control conductor 583 of which one end is connected to the first bank contact in the C bank of tens switch TS while its other end is connected to the special service unit Figs. 6, 7 and 8. N a circuit, either automatic or numerical is closed or prepared for the stepping magnet of units switch US in this instance, that is this last mentioned switch is not moved out of its normal position on code or conference calls.

The special service unit has a line finder CF, Pig. 7, associated therewith and when the special service unit is seized over conductor 533 this line finder is caused to search for the calling subscribers line. It will be noted from Fig. 7 that the special line finder CF which may be of the same type as the regular line finders LF, also has a fourth or EC wiper and contact row, the arrangement being such that the EC contacts of the special line finder are strapped to corresponding bank contacts of the regular line finders only for those lines that are entitled to initiate code and conference calls; on all other line this EC connection between the special line finder bank and the regular line finder multiple is omitted. Assuming that the calling subscriber is entitled to code and conference calls, test relay 73 of the special line finder will operate in a circuit extending over the EC wiper and bank contact of the special finder, the aforementioned EC strapping, the EC bank contact and wiper of the regular line finder and release relay36tl,.Fig. 3. Consequently the wipers of this finder CF .aresarrested, .the calling number of the special service unit is guarded and the calling bridge relay 770 of this unit switched through directly to the calling subscribers line by way of the wiper and contacts of the special line finder to the exclusion of the finder-connector link, this last mentioned link being released and thereby rendered available toother calls.

After the calling line has been switched through to the special service unit, dial tone which was previously returned from the finder-connector link after the regular line finder had originally found the calling line and was then disconnected upon the calling party dialing the first digit, is now again returned from the special service unit as an indication to the calling party that he may proceed with the dialing of the further digits required for the completion of code or conference calls. Should a calling party not entitled to code and conference call services attempt to gain access to the special service unit by dialling 1, the special line finder due to the absence of the above mentioned EC strapping will continue its hunting movement and since the calling subscriber thus fails to receive dial tone after dialing the first digit 1 he will abandon his call upon noticing his mistake. It may be noted that since the circuit means for granting the code and conference call privileges are difierent from those for providing the executive right-of-way privileges referred to above a subscriber may be given the one or the other or both privileges as desired.

It Will now be assumed that a subscriber upon making a regular call to a wanted party has received no answer due to this last mentioned party being absent from his telephone. For this purpose the calling subscriber assuming that he is entitled to code and conference call services will replace his receiver and upon again lifting his instrument from the hookswitch dial 1 to establish connection with the special service unit as just described. Upon receiving dial tone from this unit the calling party will then dial two digits into the special service apparatus which correspond to the special code assigned to the desired party. it will be noted from an inspection of Figs. 8 and 9 that the special service unit contains two register switches, S1 and S2, these two switches being 11- position rotary stepping switches with three wipers and contact rows each, and on code calls these switches are set in accordance with the last mentioned two digits respectively. The code call sender comprises a finder switch S3 which is assumed to be a 26-positi0n rotary stepping switch having 3 wipers and contact rows. As shown in Figs. 8 and 9 certain contacts in the B and C banks of sender switch S3 of the code call sender are connected to the first five contacts in the A banks of selector switches S1 and S2 by way of two groups of five marking conductors respectively, whereby 5 5 =25 two-digit codes may be provided for. In this manner any twenty-five of the maximum number of eighty parties corresponding to the ultimate capacity of the switchboard assumed herein may be assigned a special twodigit code, each of these two digits being either a l, 2, 3, 4 or 5. Upon positioning of selector switches S1 and S2 in response to these two digits code call switch S3 is automatically conditioned to actuate a number of code call sounders such as 983 and 984 which are strategically distributed throughout the establishment to sound the code determined by the setting of selector switches S1 and S2. Each of these codes then consists of two series of signal elements, the first series comprising a number of signal elements corresponding to the first of the aforementioned two digits and the second series comprising a number of signal elements corresponding to the second of these digits with a separating interval between the two series. The transmission of this code is automatically repeated by the code call sender until the called party responds to the code call as will now be described.

Upon hearing his characteristic code the called party in order to enter into communication with the calling party will dial the code call answering number from the nearest telephone. As will be seen from Figs. and 7 there is provided a code call answering trunk comprising conductors 531, 582 and 584. This trunk is connected at its one end to position of the tens switch TS of all line finder connector links and is terminated at its other end in the special service unit.

When this code call answering trunk is seized responsive to the tens switch of an idle link being set on its 10th position upon the called party dialing 0, a loop is placed across the talking conductors of the answering trunk in the special service unit so that the ring is cut off and the call switched through in the connector and the code call sender stopped after the completion of the code just being sent. In this way a talking connection is established extending from the party that originated the code call, by way of special line finder CF and con densers C7 and C8, Fig. 7, connector and line finder of the link used in dialling the answering number, to the telephone from which the called party answered the call. It will be noted that units switch US of the connector employed in answering the code call is not required in setting up the answering connection; this switch accordingly remains in its normal position.

Referring again to Figure 9, relays 940, 950 and 960 have been provided to condition the code call sender for the transmission of a code alarm under the control of some alarm actuating means, such as non-locking key 932. which may be mounted in a suitable location, for instance near a watchmans or firemans desk. When this key is operated the code call sender is conditioned to actuate the code sounders in uniformly spaced intervals. once for every step of sender switch S3, to notify the personnel of the establishment in question of the existence of an alarm condition such as a fire. The regular calling trunk to the special service apparatus is ren dered busy during the transmission of a special code alarm.

Should a code call be in process of transmission at the time the special code alarm key is actuated, the code call sender will complete the particular code cycle already begun but will then transmit the special alarm signal in preference over the code call signal. The sounding of the alarm signal is discontinued after sender switch 53 has completed one revolution, and if the party who originated the regular code call has not abandoned the call in the meantime and this last-mentioned call is still unanswered the transmission of the regular code will automatically be resumed by the code call sender.

Referring now to Figure 1 there is shown associated with the lines of subscribers A, B and C each a cut through relay, the three relays in question being indicated by reference characters 100, 110 and 120, respectively. Each of these relays functions when a conference call is being set up to a fixed group of stations, such as B, to switch the line of the station with which the relay is associated, from the regular line equipment, that is line and cutotf relay 146 in the example assumed, to the associated conference relays, 210 and 235 in the present example, shown in Fig. 2. As may be seen from the last mentioned figure a set of two of these conference relays is provided for each of subscribers A, B and C, one of the two relays of each set functioning as a ring cut-off relay and the other as a battery feed relay on conference calls to the associated station.

As will be clear from Figures l and 2 each of the cutthrough relays is controlled by a make contact of at least one of the conference group gang relays 270, 275 which are selectively operable over conductors 262, 263 connected to contacts 6 and 7, repectively, in the A bank of selector switch S1, Fig. 8, of the special service unit. As illustrated in the drawings, the arrangement is such that if the first fixed conference group is selected and gang relay 270 accordingly operated, cut-through relays and 110, respectively associated with substations A and B are operated to make contacts 271 and 272, respectively of the last mentioned gang relay; and that if the second fixed group is selected and therefore gang relay 275 operated, cut-through relays and 120, respectively associated with substations I3 and C are operated from make contacts 277 and 276, respectively of this latter gang relay. it will thus be seen that the subscriber at station A is a member of conference group No. l, the subscriber at station C t member of conference group No. 2 and the subscriber at station E a mcmber of both groups 1 and 2. It should also be noted that while only two conference groups have been shown equipped in Figures 1 and 2 a total of five groups could be provided in the instant embodiment in which case the windings of the five corresponding gang relays would be respectively connected to positions 6, 7, 8, 9 and 1-) in the A bank of selector switch S1 as indicated in Fig.

It will further be noted from Figure 1 that while subscribers A, B and C thus are all members of a conference group, the other three subscribers A, l1 and which are connected to the same line and cut-off relays 130, MO and 159, respectively, are not members of a conference group and cannot therefore receive confer ence calls. This is due to the fact that each cut-through relay such as lit) when operated functions to switch only one station of the associated party line, in the instant case station B, from the line and cut-off relay, H0. and the automatic switchboard to the conference relays, 21d and 7.35, Figure 2, whereas the other station, ll. on the party line remains connected to the line and cutoff relay and to the switchboard. However, ismuch as code and conference call privileges are granted in the instant embodiment on a line rather than party basi namely by virtue of the strappings iii), and 390 be tween the EC bank of special line finder Cl, l 7, and the EC bank of regular line finders LF, Fig. 3. all six subscribers A, A; B, B; C, C are enabled to initi' ated conference calls. This arrangement is especially advantageous where one of the parties such as B on a party line is an executive and the other, l3, his secre tary because it makes it possible for the secretary to set up a conference for the executive although she herself is not a member of the conference group. The specific arrangement shown in Fig. 1 also enables the secretary, say B, to initiate regular telephone calls while the executive, I, is engaged in a conference into which he has been called either by his sec etary or by some other privileged subscriber.

As will be understood from the foregoing explan tion, the privileges of the substations illustrated in i i 1 thus are as follows: Subscribers D and l) are party line subscribers without any special privileges. Subscribers A, B and C, and A, B and C are privileged to initiate code and conference calls. Subscribers A, l3 and C are furthermore equipped to receive conference calls, namely subscriber A in group 1, subscriber C in group 2 and subscriber B in groups 1 and 2. Sub scriber A, in addition i privileged to cut in on busy lines. As pointed out above subscriber is enabled to answer a code call.

In order to briefly explain the functioning apparatus described herein in the handling of cnce calls let it be assumed that the SUHUUJ at substation B wishes to set up a conference bctv. en the members of conference group 2. this group including the executives at substations B and C. To this end the secretary upon lifting her receiver will first dial 1" to connect herself with the special service apparatus exactly as explained above for a code call. Accordingly, after the special line finder has found the calling line the calling party is connected via lin;-v tinder CF to calling bridge relay 77d of the special service unit while the link used in setting up the connection to this unit is released. Upon receiving dial tone from the special service unit the calling subscriber then of the conferascents proceeds to dial 7. In response to the receipt of this digit selector switch S1 is set on its 7th contact to which the Winding of gang relay 275, Fig. 2, is connected. The circuit to this gang relay is closed in the special service unit without the receipt of a 3rd digit, selector switch S2 remaining in its normal position in the case of a conference call.

Operation of gang relay causes the operation of the cut-through relays such as 116 and 126, Fig. l, of the subscribers that are members of conference group No. 2. Each of these cut-through relays oper ating transfers the associated station from the regular switchboard equipment to talking conductors such as 182, 183 or 192, 1% and guards the control lead such as 186, 196 from connector banks, whereby the party line in question is busied to regular incoming we.

Ringing current is now transmitted thror .31 the l. or winding of relay 2 5 to static E o r ugh the lower winding of to s .t When the [su scriber, at station E, lifts his relays 216 and 235 operate in succession to cut and switch the subscriber by way of cm isers C13, C14 through to conference talking co .ctors 265, 266, talking battery to subscriber B be lied from relay 235. When subscriber C lifts receiver in answer to the call, relays 235i and operate and function in a simil r manner.

it wil be noted from Figs. 2, 8 and 7 that the conference Lo. ing conductors 26S and Z 6 are switched through to the talking wipers of specialline finder CF by way of make contacts of relay which is operated on conference calls, among others to busy the code call answering trunk, and also by way of make contacts of release delay relay $11 which is controlled by calling bridge relay 77d of tr e special service unit. in this manner the calling party, in this instance the secretary at station E, can converse with the members of the selected conference group as each lifts his telephone, in spite of the fact that the secretary does not belong to this group. At the end of the conference the aforementioned relay Fig. 3, remains operated under the joint control of calling bridge relay 779 and all the battery fe d relays such as 235, 24 of the conference group This insures that both the calling and code Cull answering trunks terminating in the special service 't remain guarded until all the members of the conf 1P5 group and also the conference originating party have replaced their receivers.

Should a member of the conference group to be called, for instance the executive at station E, originate a conference call himself the operation is similar to the one just described except that in this case the calling party is disconnected from the switchboard as soon as his cutthrough relay such as 11%) operates. As a consequence the calling party is connected to the conference talking path directly by way of the make contacts 114, 115 in the assumed example, of the cut-through relay while calling bridge relay 771) and associated release delay relay 816 in the special service unit restore to normal. However, relay 86% remains operated under the control of the battery feed relays, Fig. 2, and thereby holds the special service unit guarded as before until all the members of the conference group have retired from the conference. It was described above how the transmission of a regular code call is discontinued or suspended on actuation of special code alarm key 932, Fig. 9. While, therefore, the special code alarm is arranged to override a code call it does not override a conference call but the special service apparatus is designed so that a special code alarm may be initiated and transmitted while a conference is being held. In this case the calling trunk to the special service apparatus will not be unguarded until both the special code alarm the conference have been terminated.

Call from substation D to substation C Having described the operation of the telephone system illustrated in the drawings in general terms, a more detailed description of this embodiment of the invention will now be given.

Let it beassumed first that the subscriber at substation D, Fig. l, wishes to make a regular call to the subscriber at substation C. When the subscriber at station D lifts his receiver the following loop circuit is closed for line and cut-off relay ground, contact 163, subscribers loop, contact 161, upper and lower windings. of relay 160 in series, battery. The upper winding of relay 160 which, as previously mentioned, is of the 2-step type is a resistance winding and the relay is so designed that when the lower winding of relay 160 is energized with the resistance of its upper winding in series the armature of the relay is attracted only sufficiently to cause its preliminary or x contacts 162 and 165 to be closed. Thus partially operated, relay 160 at its contact 162 prepares the line finder test circuit and at its contact 165 closes ground to the distributor start conductor 190.

As the distributor, Fig. 6, is of the preselecting type, wipers 665 and 606 of distributor switch D8 will normally rest on contacts associated with an idle finder-connector link in which case ground is absent from guard conductor 667 and wiper 605. Under this assumption the following circuit is closed for distributor start relay 616 in series with magnet 675 of the distributor switch: ground, contacts 164, 165, Fig. 1, distributor start conductor 190, contact 602, Fig. 6, winding of relay 610, contacts 601 and 676, stepping magnet 675, battery. Magnet 675 cannot operate in series with the winding of relay 610 but as the magnet winding is of low resistance compared with that of relay 61th this last-mentioned relay operates. Relay 61d upon operating, at its contact 611 opens a point in an alternative circuit of stepping magnet 675; at contact 612 opens a point in a kick-off circuit to magnet 675; at contact 613 'the relay closes an obvious circuit to the lower winding of relay 620; at contact 614 relay 610 closes a multiple ground to the winding of alllinks-busy relay 6%; at contact 615 it prepares a line finder test circuit extending through the upper winding of relay 650; and at contact 616 it closes a pre-energizing circuit through the lower winding of the last-mentioned relay, this lower winding, however, not being strong enough to cause relay 656 to operate at this time. The aforementioned preenergization of relay 650 causes this relay to operate quickly upon the line finder test wiper encountering battery potential so that when the line finder happens to stand on the calling line, unnecessary starting of the line finder is avoided.

Upon energization of its lower winding relay 620 operates with a certain delay which is due to the short circuit of its upper winding at contact 634. After relay 621 has operated it closes at its contact 621 an obvious circuit to the winding of slow-to-operate relay 630 and at its contact 622 prepares a circuit for timing relay 660. When relay 630 operates a short time after energization of its winding, it closes the following circuit for start relay 320 of the pro-selected link, Figures 3-5: ground, contact 631, wiper 666 and bank contact of distributor switch DS, conductor 647, start relay 320, Fig. 3, battery. At contacts 632 and 633, relay 631i closes a point in two incomplete circuits for distributor switch magnet 675, respectively; at contact 634 the relay opens the short circuit across the upper winding of relay 626 to render this lastmentioned relay fast to operate; at contact 635, relay 630 closes another multiple ground to the winding of all-linksbusy relay 660; and at contact 636, the relay closes a point in the circuit of line finder magnet 370.

When line finder start relay 320 operates, it closes the following circuit for calling bridge relay 330; ground, lower winding of relay 330', contact 321, resistance 387, upper winding of relay 330, battery. Relay 330 upon operating, at its contact 322 also prepares a circuit to the 11 winding of line finder switching relay 310; at contact 323 closes another point in the aforementioned line finder test circuit; and at contact 324 completes the following circuit for line finder magnet 370: ground, contacts 636, 641, 652, Figure 6, conductor 617, contacts 324 and 315, Fig. 3, line finder stepping magnet 370, battery.

Calling bridge relay 33G, upon operating in the aforementioned circuit, at its contact 33 closes an obvious circuit to the winding of release delay relay 340 which accordingly operates; and at contact 332 opens a point in the connector impulsing circuit. Relay 340 in oper ating at its contact 341 closes a point in the last-mentioned impulsing circuit and at contact 342 causes the operation of relay 410, Fig. 4, by way of conductor 391. Relay 410 in thus operating at its contact 411 closes ground through contact 491 to permanent alarm con ductor 445; at contact 412 closes a point in the dial tone circuit; at contact 413 grounds the start conductor 433 for starting a common ringing generator and interrupter, tone and timer apparatus which is not shown in the drawings; at contact .14 relay 410 closes operating or holding ground to various incomplete circuits; at contact 415 it prepares a holding circuit for line and cut oil relay 169; at contact 416 it opens a point in the tens switch homing circuit; at contact 417 it closes a point in the circuit for slowrelease relay 460; at contact 318 it opens a point in an alarm circuit extending over conductor 429; and at contact .19 it prepares a circuit for relay 520.

Reverting now to line finder LF, Figure 3, the stepping magnet 370 of this finder upon its energization closes its contact 371 thereby completing a circuit extending over conductor 607 to interrupter relay 640, Figure 6. The latter relay upon operating at its contact 641 opens the above-traced operating circuit for line finder magnet 370 to cause this magnet to release and thereby cause the line finder to advance its wipers one step. Also upon the release of line finder magnet 37% the circuit of interrupter relay 640, Fig. 6, is opened at contact 371 so that relay 640 restores, reclosing at its contact 641 the operating circuit of line finder magnet 371]. As a result, this magnet is again energized and contact 371 recloses the circuit of interrupter relay 641]. This relay upon operating again opens the circuit of line finder magnet 370, thereby causing this magnet to reopen contact 371 and cause the wipers of line finder LF to be advanced another step. The foregoing interaction between magnet 370 and interrupter relay 646 continues until the wipers of the line finder have been positioned on the set of bank contacts associated with the calling line. When these contacts have been reached test relay 653, Fig. 6, and line and cut-off relay 160, Fig. l, which are both pro-energized as above described, operate in series in the following circuit: ground, contact 615, upper winding of relay 650, conductor 627, contact 323, Fig. 3, C wiper 333 and bank contact of finder switch LF, conductor 356 of cable C170, contact E62, Fig. 1, lower winding of relay 160, battery.

Relay 650 upon operating at its contact 652 opens a point in the above-traced circuit of line finder magnet 37G to prevent the re-operation of this magnet; at its contact 655i the relay closes the following circuit for line finder switching relay 310: ground, contacts 636, 641, 651, Fig. 6, conductor 637, contact 322, Fig. 3, winding of switching relay 310, battery; at contact 654, relay 65% opens a point in the holding circuit for timer relay 67ft, and at contact 653 it actuates total call meter 685 over an obvious circuit. When switching relay 310, Fig. 3, operates, it switches the calling line through to calling bridge relay 330, namely by way of talking conductors 136, 146 of cable C170, bank contacts and talking wipers 381, 382, of line finder LF, and contacts 3li and 312; this establishes a holding circuit for calling bridge relay 330 independent of contact 321 of start relay 32th and causes dial tone to be connected to the calling line by way of condenser C2, conductor 389, contacts 412, 492, Fig. 4, condensor C5 and dial tone conductor 446. At contact 313, relay 310 closes a substitute circuit for line and cut olt relay extending from ground at contact 4-15, Fig. 4, by way of conductor 3%, contact 313, and the C wiper 383 and C bank contact of line finder LF, Fig. 3; at contact 314, relay 310 completes a holding circuit for itself, this last-mentioned circuit extending from ground at contact 415, Fig. 4, by way of conductor 390, contacts 361 and 314, Fig. 3, and the winding of relay 310 to battery; at 315, relay 313 opens another point in the circuit of line finder magnet 370; at contact 317 the relay opens a point in the circuit extending over all-trunks-busy conductor 337; and at contact 316, it closes ground to link guard condoctor 667.

The last mentioned ground on link guard conductor 667 extends over the bank contact and wiper 605 of distributor switch DS and contacts 632, 676 and 601 to the upper terminal of the winding of distributor start relay 610 whereby this relay is caused to release. Ground on link guard conductor 667 also causes distributor switch magnet 675 to be energized over a part of the circuit path just traced. Relay 610 in restoring at its contact 611 closes an alternative short circuit of this relay which is independent of contact 676 of the distributor switch magnet; at contact 612 the relay closes an alternative circuit for the last-mentioned magnet, this circuit extending from ground through contacts 612 and 633 and magnet 675 to battery; at contact 613 the relay opens the circuit of relay 620; at 614 removes a multiple ground from the winding of all-trunksbusy relay 600; at 615 opens the line finder test circuit cittcnding through the upper winding of test relay 650; and at 616 opens the circuit of the pre'cnergizing winding of this relay. Test relay 6% in restoring at contact 652 closes a point in the circuit of line finder magnet 37% but this circuit can no longer be completed as it is open at contact 32 4 of switching relay 320. ltclay 63.0 in restoring at contact 622 disconnects timer relay 660 from time pulse conductor T1 and at contact 621 opens the circuit of relay 630 so that this relay also restores.

When relay 630 releases, ground is removed at contact 631 from start conductor 647 so that line finder start relay 320 restores. At contacts 632 and 633 the two aforementioned circuits to distributor switch magnet 675 are opened so that this magnet in restoring closes its interrupter contact 676 to again prepare the operating circuit of start relay 610 and advances the wipers of distributor switch DS to the next set of contacts; at contact 634 a short circuit across the upper winding of relay 62.0 is reestablished in preparation for the next call; at contact 635 a multiple ground is removed from all-trunks-busy relay 6%; and at 636 another point in the circuits for line finder switching relay 310 and line finder magnet 370 is opened. Prior to the circuit operations last described, line and cut-otl relay 169, Fig. l, was fully operated in the aforementioned line finder test circuit, whereby contacts 161, 163, respectively disconnected battery and ground from the caliing line in the line equipment and contact 16-!- disconnected ground from conductor and the lower terminal of the winding of distributor start relay 610 provided no other line was in calling condition at this time.

Reverting to the step taken by distributor switch D5 upon release of relay 630 as just described it will be understood that switch D8 will take no further steps provided no ground potential is encountered by its wiper 665 upon completion of this step, i. 0. provided the finder-connector link connected to the corresponding second set of bank contacts of distributor switch DS is idle at this time. On the other hand should this link be busy, ground on the guard conductor of this link will cause d1stributor switch magnet 675 to be re-energized over a circuit extending from ground on this conductor; wiper 6%, contacts 611, 66:, 676 and magnet 675 to battery. Magnet 675 upon operating at its interrupter contact 6'76 opens the last-mentioned circuit so that magnet 675 restores thereby advancing its wipers to the next following set of bank contacts. In this manner the wipers of distributor switch D are automatically advanced until an idle link having no ground on its guard conductor is found. Should the link connected to the last position of the distributor switch be found busy, switch [)5 is advanced to its home position, but since in this last-mentioned position cit-normal springs 691 are closed, ground at the off-normal springs will immediately cause the switch to be advanced to its first position in which it is shown in the drawing.

if all links become busy at time other than while the distributor, Fig. 6, is in start condition, ground is removed from common all-trunks-busy conductor 657 and the normally operated all-links-busy relay 6% restores. As a result a point in the automatic stepping circuit for magnet 675 is opened at contact 6% so that unnecessary stepping of distributor switch DS is avoided; at contact 6% start conductor 1% is disconnected from the lower terminal of the winding of distributor start relay 616 to prevent the seizure of the distributor in a call that may originate during the all-trunks-busy condition; and at contact 693 an obvious circuit is closed to all-trunks-busy meter 6% whereby the all-trunks-busy condition is registered.

Reference has been made above to a kick-off circuit extending over contacts 612 of relay 610 and make contact 633 of relay 636 to distributor switch magnet 675. This circuit is used to advance the wipers of the distributor switch to the next position if a call is abandoned before the line finder, for example because of a faulty condition, has found a calling line, that is before switching relay 316 could operate to energize magnet 675 by way of guard conductor 667. This prevents the same line finder from being used on successive calls under the last-mentioned condition.

Should the line finder upon the initiation of a call fail to find the calling line due to some faulty condition and the calling party fail to abandon the call within a predetermined time, the same result would be brought about by means of a ground pulse received from the common timer, not shown, by way of pulse conductor P2 and contact 661 of relay 660. More specifically, if relay 626 is still operated by the time a ground pulse is received over pulse conductor P1, relay 666 will operate in a circuit extending from ground on this conductor, contacts 664 and 622 and the winding of relay 660 to battery. Relay 660 in operating at its contact 661 closes pulse conductor P2 to the winding of distributor switch magnet 675'; at its contact 662 closes the winding of relay 67d to pulse conductor P3 by way of contact 672; and at contacts 663, 66 itransfers the winding of relay 660 from ground on pulse conductor P1 to ground on start conductor 1%. When ground after a certain time interval is next closed to pulse conductor P2 in the timer, this ground will cause the energization of distributor switch magnet 675 by way of contact 661; and at the end of this ground pulse the magnet will be deenergized again whereby the wipers of the distributor switch are advanced one step.

Should the calling condition on start conductor 1% persist and relay 660 still be operated when ground, after another time interval, is connected to pulse conductor P3, this last-mentioned ground will cause the operation of relay 670 by way of contacts 662 and 672. Relay 67C upon operating at its contact 673 closes an obvious circuit to alarm lamp 691 and at contacts 671, 672 transfers the winding of relay 67th from ground on pulse conductor P3? to ground on contact 654 of test relay 655). This alarm condition will be removed when the line finder finds the calling line so that test relay 650 in operating opens the holding ground of relay 67% at contact 654, permitting the latter relay to release. if the call is thus completed the holding circuit of relay 66% also is opened at contact 622 when relays 61d and 62h restore as a result of the operation of finder switching relay 310. it will be seen that because of the slow-operating characteristic of relay 624) in view of the short circuit across its upper winding sufficient time is allowed for relay 66% to restore even though a new call that might be waiting at this time should cause relays 610, 626 and 636! to go through another operating cycle.

Reverting again to the operation of the finder-connector link, it will be recalled that relays 310, 330, 340 and 416 are in operated condition subsequent to line finder LP finding the calling line. On hearing the dial tone, the calling party, D, will now proceed dialling the first or tens digit 7 of the called partys number. Calling bridge relay 33h accordingly responds to the impulses received over the calling line by restoring and re-operating seven times in quick succession. Each time relay 313i restores it closes, at its contact 332, the impulsing circuit traced below, and at contact 331' opens the circuit of relay 3%. Due to its slow releasing characteristic this last-mentioned relay stays operated throughout the impulse series. Upon the first release of calling bridge on line relay 336 the following circuit is closed to relay 460: ground, contacts 332 and 341, Fig. 3, conductor 394, contacts 425, 488, 417, Fig. 4, winding of relay 466, battery. Relay 460 in operating at its contact 462 opens a point in the circuit of relay 4% and at its contact 261 causes the operation of relay 456 over an obvious circuit. The last-mentioned relay at its contacts 451, 453 transfers the C wiper 565 of tens switch TS from the lower winding of relay 4% to the winding of busy relay 420; and at contact 454 closes a locking circuit to its winding independent of contact 425 of the busy relay. Also at contact 332 the following impulsing circuit to stepping magnet 54s of tens switch TS is closed: ground, contacts 332 and 341, Fig. 3, conductor 394, contact 425 or 454, 488 and 495, Fig. 4, conductor 467, magnet 540, Fig. 5, battery. Motor magnet 546 is energized over this current. When line relay 33% upon reoperating at the end of the first impulse opens its contact 332, magnet 54% is deenergized whereby the wipers of tens switch TS are advanced from the home position to position 1 of this switch. In this mannerthe wipers of the tens switch are advanced one step for every restoration of line relay 3%. Relay 466' and consequently relay 45d stay operated during the series of impulses because of the slow-releasing properties of relay 466.

At the end of the impulse series the wipers of tens switch TS rest on position 7 or" the switch and relay 46th releases as the circuit is permanently opened at contact 332 of relay 3%, this latter relay remaining in operated condition at the end ofthe first digit. Relay 469 upon restoring at its contact closes the following circuit for relay 4%: ground, bank contact and A wiper 561 of tens switch T S in position 7, conductor 4 53, contact 462, Fig. 4, winding of relay 490, battery. When relay 4% operates it opens at its contact 491 the permanent alarm circuit extending over conductor 445; at contact 4%, relay 4% disconnects dial tone from the calling line; at contact 494, relay closes a locking circuit for its winding independent of contact 462 of relay 460; at 495, relay opens another point in the above-traced impulsing circuit; at i e relay closes a multiple guarding ground extending over conductor 495 to guard conductor 667, Fig. 3; at contact 497 the relay opens another point in the all-trunks-busy circuit; at 498 it prepares an alarm circuit extending over alarm conductor 429 for the purpose of supervising the release of tens switch TS at the end of the call; and at contact 493 the relay completes the following circuit to relay 520: ground, contacts 414 and 593, Fig. 4, conductor 466, B wiper 562 and 7th bank contact of tens switch TS, Fig. 5, home bank contact and wiper 577 of units switch US, conductor S, contact 419, Fig. 4, conductor 457, relay 5 0, Fig. 5, battery.

As will be seen from the strapping of the B bank of tens switch TS, relay 520 which serves to position units switch US on its llth position as described hereafter is caused to operate only when tens switch TS has been arrested in any of positions 6, 7, 8 or 9 of the switch. Relay 520 in operating at its contact 521 opens a point in the test circuit extending over C wiper of the tens switch; at its contact 522 the relay closes the following circuit for relay 510: ground, contacts 414 and 4-93, Fig. 4, conductor 466, contact 522, Fig. 5, winding of relay 510, battery; at contact 523 the relay opens a point in the impulsing circuit for units switch US; at contact 525, the relay opens a point in the homing circuit of the units switch; and at contact 52-1 the relay extends ground at the left hand terminal of its winding by way of interrupter contact 551 to the Winding of stepping magnet 550 of units switch US to energize this magnet. When relay 510 operates as mentioned above it closes a locking circuit for itself at its contact 511; at contact 51.2 it opens another point in the homing circuit of the units switch; at contact 513 it opens a point in the homing circuit for tens switch TS; and at contact 51-1 it closes a point in the impulsing circuit for the units switch.

When magnet 550 of units switch US is energized due to the aforementioned closure of contact 524 it opens its own circuit at its interrupter contact 551. When the magnet is thus dcenergized it advances the wipers of the units switch from its normal or home position to position 1 and re-closes its interrupter contact 551. In position I of the units switch the off-normal springs 578 of this switch are actuated so that off-normal relay 530 is caused to operate over an obvious circuit. This relay in operating at its contact 531 closes a point in the units switch homing circuit; at 532 it closes a multiple ground extending over conductor 395 to link guard conductor 667; and at contact 533 closes a multiple ground to conductor 456, this ground serving to supervise the release of units switch US at the end of the call. When stepping magnet 550 recloses its interrupter contact 551 as mentioned above this magnet is again energized so that the magnet in re-operating again interrupts its own circuit by renewed actuation of interrupter contact 551. The magnet is thereby deencrgized again, interrupter contact 551 recloses and the wipers of the switch are accordingly advanced to position 2.

This automatic stepping action of units switch US continues until the switch reaches position It at which time wiper 577 disengages itself from the bank contacts of the units switch that are strapped to contacts 6-9 in the B bank of the tens switch as shown in Fig. 5. As a result the above automatic stepping circuit of magnet 559 can no longer be re-closed and the circuit of relay 520, which likewise extends over the C3 wiper and bank of units switch US, also is opened so that this relay releases. Relay 520 upon releasing at its contact 5.2.1 re-closes a point in the testing circuit extending over wiper 565 of the tens switch; and at its contact "24 opens another point in the last-mentioned automatic stepping circuit for units switch a.

The circuit is now in condition to receive the second or tens digit dialled by the calling subscriber. in response to this digit which is assumed to be a 5, line relay 330 will release and re-operate five times in quick succession. Again relay 3-10 remains operated during the brief interruptions of its circuit at contact 331. On the first closure of contact 332 upon receipt of the first impulse or" this series the aforementioned circuit For relay 460 again is closed and this relay in operating at its contact 461 again causes the operation of its slave relay 450, whereby C wiper 165 is again transferred from the lower winding of connector switching relay lfitl to the 1.1) winding of busy relay 420. Because of the slow release characteristic of relay 460, relays 466 and 457i again remain operated for the duration of the impulse series. Closure of contact 332 also completes the following impulse circuit to stepping magnet 550 of units switch US: ground, contacts 332, 34ft, Fig. 3, conductor 3%, contacts 425 or 45- 488, conductor 469, contacts 5M and 523, Fig. 5, magnet 550, battery. When ealli bridge relay 33G re-opcrates at the end of the first impulse the last traced impulse circuit to magnet 550 is opened so that this magnet in releasing advances the wipers of the units switch from start position l1 to position 112. in this fashion the wipers of the units switch are advanced one step for each release and re-operation ol relay 330 so that at the end of the impulse series, when relay 33H remains in operated condition, t.c wipers of the units switch come to rest on position 16 of this switch.

With tens switch TS positioned on its position 7 and units switch US set on its position 5 it will be noted that the talking wipers 563 and 564 of the tens sw'tch are respectively connected by way of conductors 519i and 592 to the upper talking wipers 57l and 572 of the units switch, and that these last-mentioned wipers in turn connect with talking conductors 191 and l94- which lead to the party line shown as the third from the top in Fig. 1. it will also be noted that a line reversal has been introduced in the connection between the talking wipers ol the tens switch and those of the units switch, that is the negative talking wiper 571. of the units switch is connected to the positive talking wiper 564 oi". the tens switch and the positive talking wiper 572 of the units switch is connected to the negative talking wiper 563 of the tens switch. This insures that ringing current is projected over the positive side of the called line as will explained hereinafter. Moreover, it will be understood that the C wiper 565 of the tens switch is connected by way of conductor 395 and the C1 wiper 575' of units switch US with conductor 196 which extends to the lower winding of line and cut-oft relay 150, Fig. 1, associated with the called party line.

Assuming first that this called line is idle, battery potential through the lower winding of line and cut-oil relay will be encountered by the Cl. wiper of units switch US. Accordingly when relays 460 and 4-50 release successively at the end of the second impulse series the following circuit is closed for the lower winding of connector switching relay and line and cut-oli relay 150 in series: ground, contacts 414, 435 and 422, Fig. 4, lower winding of relay 480, contacts 85 and iii, conductor 465, contact 521i, Fig. 5, wiper 565 and 7th iJllnlZ contact in the C bank of the tens switch, conductor i595, wiper 5'75 and the 16th contact in the Cl bank of the units switch, conductor 196, contact 128, Fig. l, lower winding of relay 150, battery. Both relays -litl), Fig. l, and 150, Fig. l, operate in this circuit. Line and cut-oil relay 1% in fully operating at its contacts 151, 152. d'." connects battery and ground from the linc in the line circuit. During the armature travel of relay 156 there will be a short time interval during which preliminary contact is already closed while contact IS-t is not open as yet. During this short interval ground will be applied to the distributor start conductor 19! so that start relay 610, Fig. 6, may operate momentarily. However as relay 620, due to the short circuiting of its upper winding, and also relay 631'} are slow in operating such a momentary operation of relay 616 will not cause a line finder to be started under this condition.

When switching relay .80 operates in the connector as just described it closes a locking circuit for itself at its preliminary contact 434, this circuit extending from ground through contacts and and the upper winding of relay 436 to battery. At its contact llil relay 4th} connects ring-hack tone to the negative side of the calling line over the following circuit path: battery-connected ringing generator, not shown, conductor lSL,

lower winding of relay 470, ring-back'tone condenser C3, contacts 431, 481 and 472 and from there through condenser C1 to the calling partys telephone. At contacts 482 and 483 of relay 480 the following ringing circuit is closed for the ringer at. substation C, Fig. 1: batteryconnected generator, not shown, conductor 459, lower winding of relay 470, contacts 471 and 482, conductor 447, wiper 563 and associated 7th bank contact of the tens switch, Fig; 5, conductor 592, positive talking wiper 5.72 and associated 16th bank contact of units switch US, conductor 194, positive side of the line of subscriber C and fromv there through the condenser and ringer at station C to ground. Relay 480, furthermore, at its contact 486 closes direct ground to C wiper 565 to guard the calledlineagainst intrusion;,at its contact 485 disconnects its lower winding from the test circuit extending over the last-mentioned C wiper; at contact 487 opens a point in the homing circuit for tens switch TS; at. contact. 488 opens a point in the impulsing circuit for units switchmagnet 550 and at contact 489 opens a point in the homing circuit of this last-mentioned switch.

Upon hearing the ringing signal the subscriber at substation C answers the call by lifting his receiver from the switchhook. As a result ring cut-oif relay 470 which could not operate in response to the ringing current alone will now operate because of the closure of the direct current loop over the called subscribers line. This loop extends from the aforementioned battery-connected generator through most of the circuit path just traced, the

closed hookswitch contacts at substation C, conductor 191, bank contact and wiper 571 of the units switch, conductor 591, bank contact and wiper 564 of the tens switch,v conductor 449 and contacts 483 and 474 to ground. Upon its energization over the last-mentioned direct current loop relay 470 closes its preliminary contact 476, whereby the upper winding of relay 470 is energized in a circuit extending from ground through contacts 486 and 476 and the upper winding of relay 470 to battery. Thus energized over its upper winding relay 470 operates fully thereby opening the ringing circuit at its contacts 471, 474 and switching the called line through to battery feedimpedance 465 at contacts 473, 475. At contact 472, ring-back tone is disconnected from the calling side of the connection. The calling party at substation D and the called party at substation C may now converse with each other by way of condensers C1 and C2, the calling partys transmitter being supplied with direct current through the windings of relay 331) and the called partys transmitter through the windings of impedance 465.

, Release of the connection is under the sole control of the calling party. Thus, if at the end of the call the party replaces his receiver, relay 330 restores causing slow release relay also to release. Relay 340 in restoring in turn causes the release of its slave relay 410. When relay 410 restores, the opening of contact 415 interrupts the holdingv circuit of line finder switching relay 310 which releases thereby removing a multiple ground from link guard conductor 667, and also interrupts the circuit of the line and cut-oil relay, 160, of the calling party sothat this relay likewise restores to normal. Also upon the release of relay 414i ground is disconnected at contact 414 from the holding circuits of relays 510, 481) and 470, whereby these relays are caused to release. With relays 51%, 484 and 410 restored the following circuit is closed for the stepping magnet of tens switch TS: ground, A bank and wiper of switch TS, conductor 448, contacts 487 and 416, Fig. 4, conductor 468, contacts 513 and 541, Fig. 5, winding of magnet 540, battery. Magnet 54h attracts its armature thereby opening its energizing circuit at interrupter contact 541. As a result magnet 540 advances its wipers into position 8 and re-closes its interrupter contact 541. In this manner the tens switch is stepped ahead until it reaches its home position. In this position the A wiper of the switch disengages the A bank, all the contacts of which areconnected to" ground, so that stepping magnet 54% cannot be energized again. As a further consequence of wiper A returning to its normal position the circuit of relay 499 is opened so that this relay restores, thereby removing a multiple ground from link guard conductor 667 and from alarm conductor 429.

With relays 510 and 48 i restores, a similar homing circuit is closed for stepping magnet 550 of units switch US, this circuit extending from ground through units switch off-normal contact 578, contacts 531' and 512, con ductor 427, contact 489, Fig. 4, conductor 428, contacts 525 and 551, Fig. 5, magnet 550 to battery. Magnet 550 in operating opens this homing circuit at interrupter contact 551 so that the magnet becomes deenergized and the wipers of the units switch are advanced from position 16 to position 17. in this fashion the switch stepsahead until it reaches its home position. Inthis home position of switch US off-normal springs-578 open and consequently the last-mentioned stepping circuit is broken sothat magnet 550 cannot here-energized. Also upon the opening of oil-normal contact 578, relay 530 releases, thereby removing ground'from link guardconductor 667 and' from alarm conductor 429. v

It will be understood from the foregoing description of the homing operation of switches TS and US, that these two switches are horned independently of each other and that their homing action is supervised by alarm conductor 429; for should one or the other of thetwo switches fail to restore to normal, relay 490 or 530, as the case may be, would be held operated and the alarm circuit kept closed over contact 498 or 433. Assuming that delayed alarm equipment is connected to the other end of conductor 429, this alarm will become effective if one or the other switch has not reached its home position within a predetermined time. It may bementioned at this point that similar delayed alarm equipment may also be connected to the far end of permanent alarm conductor 495. When this permanent alarm becomes. effective after a certain time it serves as an indication that the calling party has failed to dial within a given time after seizure of the link.

In the above description it was assumed that the line of called line C was found idle by the connector when called. Let it be assumed now that the called partys line is busy in either an incoming or outgoing call at the time the wipers of units switch US- are set on this line. In this case the control conductor 196 associated with this party line carries ground potential and as a consequence the following circuit to busy relay 420' is closed prior to the release of relay 450 at the end of the units digit: ground on control conductor 196, contact 16' in the Cl-bank of units switch US, wiper 575 of this switch, conductor 595, seventh C-co'ntact and wiper 565' of tens switch TS, contact 521, conductor 465, contact 453, Fig. 4, winding of busy relay 420, battery. Busy relay 4269 in operating at its contact 421 connects busy tone to the calling side of the connection over the following circuit path: busy conductor 499, condenser C6, contacts 421, 433, conductor 389 and from there over talking condenser C2, Fig. 3, to the telephone instrument of the calling party; at contacts 422, 423 the relay transfers ground from the lower winding of switching relay'480 to its own winding, thereby closing for itself the following holding circuit which becomes effective upon the release of relay 451): ground, contacts 414, 435, 423, 437, 442, 452, winding of relay 420, battery. At contact 424 the busy relay opens a point in the circuit of relay 360; and at contact 425 relay 420 opens a point in the numerical impulsing circuit.

Upon receiving the busy signal thecalling party will replace his receiver and thereby cause the successive release of relays 330, 340, and 410 as described above in connection with the release of a completed connection. At contact 415 relay 410 opens the circuits of relays 310 and and at contact 414 relay 410 opens the locking circuits of relays 420 and 510 so that all these relays restore to normal. With relay 510 released the above traced homing circuits for stepping magnet 540 of tens switch TS and magnet 550 of units switch US also are closed. From thereon the release of the finder-connector link proceeds in the manner described above for a completed call.

The foregoing description will make it clear how the link circuit shown in Figs. 3-5 functions when the calling party releases after the completion of a call or upon receiving a busy signal. Should the calling party abandon the call prior to dialling, line relay 330, Fig. 3, in releasing at its contact 332, closes the impulsing circuit to magnet 540 of the tens switch and slow release relay 460 in parallel. Relay 460 in operating in turn causes the operation of its slave relay 450. Subsequently relay 340 restores thereby opening the circuits of magnet 540 and relay 460 at its contact 341 and opening the circuit of relay 410 at contact 342. Relay 410 in restoring at its contact 415 causes the release of relays 310 and 160 as described above and at its contact 417 also opens the circuit of relay 460 so that the latter relay releases after a certain delay, in turn causing relay 450 to restore. Relay 410 upon releasing at its contact 416 furthermore closes the above-traced homing circuit for magnet 540 which extends over the A wiper of the tens switch TS. As soon as relay 460 restores the operating circuit for relay 490 also is closed namely at contact 462. Relay 490 at contact 496 maintains ground on guard conductor 667 and at contact 498 closes the alarm circuit extending over conductor 429 to supervise the homing of the tens switch.

If the special service apparatus is busy while the tens switch upon the calling party restoring his receiver goes through the aforegoing stepping cycle, ground encountered by wiper 565 in position 1 of this switch will operate busy relay 420 but this will cause no harm as the calling partv has hung up and as with contact 414 open no locking circuit can be closed for relay 420. Should the wiper 565 encounter ground at the control lead of the code call answering trunk when the switch is in position the closure of a circuit through the winding of relay 520 and the lower winding of relay 480 in series is avoided by the provision of contact 419 which is open at this time. As soon as the tens switch reaches its home position, magnet 540 cannot be energized anymore and the circuit of relay 490 also is opened so that this relay releases. The link circuit shown in Figs. 3-5 is thereby returned to its normal condition.

Call from substation A to substation B It will be recalled that substation A is provided with facilities for cutting in on a busy line. For this purpose a push button or non-locking key 178 is provided at this station and one spring of the make contact of this key or button is connected by way of conductor 189 to the corresponding contact in the EC bank of line finder LF, Fig. 3. The other contact spring of push button 178 is shown in Fig. 1 directly connected to ground but if desired this connection may be taken through a hookswitch contact of station A so that ground cannot be connected to conductor 189 except when the handset at this station is off the hook.

When the subscriber at station A lifts his receiver to place a regular call to substation B, finder LF of an idle link is caused to search for and connect with a calling line in the manner described above in connection with a call from substation D. It will be seen from Fig. 1 that substation B which is assumed to be the called subscriber in the present case, has directory number 42 so that the calling party upon receiving dial tone will dial 4 as the first digit. In response to this digit the tens switch TS, Fig. 5, is positioned on its fourth set of contacts as described in the preceding section. However, since at the end of this impulse series B wiper 562 of tens switch TS is arrested on its fourth rather than seventh bank contact the above-traced circuit for relay 520 cannot be closed in the instant case. When relay 490 operates upon the release of relay 460 at the end of the first digit the following alternative circuit is closed for relay 510: ground, contacts 414 and 493, Fig. 4, conductor 466, B wiper 562 of switch TS, Fig. 5, contact 4 of the B bank of this switch, winding of relay 510, battery. Relay 510 in operating at contact 511 closes a locking circuit for itself and at contact 514 closes a point in the impulsing circuit for units switch US.

A circuit is now ready for the receipt of the second series of impulses in response to which stepping magnet 550 of the units switch receives two numerical impulses over the impulsing circuit traced in the preceding section, this circuit extending from ground through contacts 332 and 341, Fig. 3, conductor 394, contacts 425 and 488, Fig. 4, conductor 469, contacts 514 and 523, Fig. 5, and the winding of magnet 550 to battery. Since the second or units digit is assumed to be 2 units switch US will be advanced in response to this digit from its home position to position 2.

It will be noted that with tens switch TS thus set on its fourth position and units switch US on its position 2, the lower set of wipers 573 and 574 of the units switch is connected up through wipers 563 and 564 of the tens switch so that connection is made through the wipers of tens and units switch in series and conductors 181, 184 with the party line including substation B and B, Fig. 1. Attention also is called to the fact that in the instant case the talking wipers of the units switch are connected to those of the tens switch without line reversal, that is negative talking wiper 573 is connected with negative talking wiper 563 and positive talking wiper 574 with positive talking wiper 564. Accordingly if the called line is idle and connector switching relay 480 operates in series with the line and cut-oi? relay of the called line as described in the preceding section, ringing current will be projected over the negative side of the called line namely in the following circuit: battery-connected generator, not shown, conductor 459, lower winding of relay 470, contacts 471 and 482, Fig. 4, conductor 447, wiper 563 and associated 4th bank contact of tens switch TS, Fig. 5, conductor 593, wiper 573 and associated second bank contact of units switch US, conductor 181, contact 113, Fig. l, condenser and ringer at called subscriber station B, ground.

The operation of the link circuit upon the answering of the call by the called party and subsequently upon disconnection of the calling party is substantially the same as described in the preceding section in connection with a call from substation D to substation C and therefore need not be described again at this point.

It will now be assumed that the party line to which the called subscriber B is connected is busy. Accordingly, after the units switch has been positioned on this line, busy relay 420 will operate and lock as explained in the preceding section so that the executive at calling substation A receives busy tone. The executive at this station now may either replace his receiver as described in the preceding section or he may cut in on the busy line by depressing his push button 178. When this push button is depressed the following circuit for relay 440 is closed: ground, make contact of pushbutton 178, Fig. l, conductor 139, corresponding EC-bank contact and EC wiper 384 of line finder LF, Fig. 3, conductor 329, contact 419, Fig. 4, conductor 328, contact 351, Fig. 3, conductor 393, winding of relay 449, Fig. 4, battery. relay 440 in operating at its contact 441 closes ground by way of conductor 387 to IL conductor 325, Fig. 3; and at its contact 442 opens the short circuit across the winding of relay 430 so that this last-mentioned relay, upon release of relay 450 at the end of the units digit, operates in series with the winding of busy relay 420 in the following holding circuit for the latter relay:

21 ground, contacts 414, 435 and 423, winding of relay 430, contact 452, Winding of busy relay 420,. battery.

Upon operating in this circuit relay 43% at contact 437 opens another point in the aforementioned short circuit across its winding; at contact 431 opens a point in the ring-back tone circuit; at contacts 432 and 434 switches the calling party through to the called line by Way of condensers C4 and C5; and at contacts 436, 435 substitutes the following circuit for the last-traced circuit including relays 43d and 420 in series: busy ground on control conductor 186, Fig. 5, CZ-bank contact and wiper 576 of the units switch, conductor 596, 4th C-bank contact and wiper'565 of the tens switch, contact 521, conductor 465, contacts 436 and 423, Fig. 4, winding of relay 430, contact 452, winding of busy relay 420, battery.

When the party at substation A subsequently releases push button 178, ground is removed from conductor 189, Fig. 1, and relay 440, Fig. 4, releases, thereby disconnecting ground from conductor 325 at contact 441. Due to contact 437 being open reclosure of contact 442 upon the release of relay 440 will not affect the operated condition of relay 430.

The executive at substation A may now converse, by way of condenser C4 and C5, with the called party at substation B while the other party with which subscriber B is connected in either an outgoing or incoming call is still on the line. On the other hand, the executive upon notifying these two parties of his desire to talk to subscriber B may hang on while the two parties mentioned finish their conversation. Subsequently when both parties in this original call have replaced their receivers ground potential is disconnected from control conductor 186 and accordingly the last-traced series circuit through the windings of relays 438 and 429 is broken. Both these relays will accordingly restore to normal and as a result the following circuit including connector switching relay 480 and line and cut-off relay 1443 of the called line in series is now completed: ground, contacts 414, 435 and 422, Fig. 4, lower winding of relay 48 d, contacts 485 and 451, conductor 465, contact 521, Fig. 5, wiper 565 and associated fourth bank contact, conductor 5%, wiper 576 and associated second bank contact, conductor 186, contact 118, Fig. 1, lower winding of relay 145 battery. Both relays 480 and 148 operate in this circuit and accordingly the bell at called substation B is now rung exactly as if this subscribers line had been idle in the first place as described above. The circuit functions upon answering and release of the connection also correspond to those described in the preceding section.

Code call from substation A to substation B As mentioned above those subscribers that are entitled to initiate code calls or conference calls, have their corresponding EC bank contacts in the banks of special line finder CF, Fig. 7, and regular line finders LF, Fig. 3, connected with each other. In the case of the line of subscribers A and A, the conductor providing this connection is designated in these figures by reference numeral 189.

Assuming that the subscriber :at station A in calling subscriber B, as described above, has obtained no answer from this last-mentioned subscriber and that this latter party is one of the subscribers to whom a code is assigned for code call purposes subscriber A, upon replacing his handset, may proceed to establish a code call to called subscriber B. In order to set up this code call the party at substation A removes his handset again from the cradle and is thereby connected with an idle finderconnector link in the manner described hereinbefore. Subscriber A then dials l as the first digit, this being the digit used for giving calling access to the special service apparatus. Dialling of the digit 1 causes line relay 340, Fig. 3, to restore and reoperate once whereby the Wipers of tens switch 1 are advanced to position 1 by way of the above traced impulsing circuit" for the tens switch. When relay 460 releases and. relay 490 operates at the end of this impulse series, special service relay 350 operates in the following circuit: ground, contacts 414 and 433, Fig. 4, conductor 466, B wiper 562 and first B contact of tens switch TS, Fig. 5, conductor 397, winding of relay 350, Fig. 3, battery. Relay 350 in operating at its contacts 351, 352, transfers the EC wiper of line finder LF from the Winding of busy cut-in relay 440 to the winding of special release relay 360. It should be noted that with the B wiper oftens switch TS inits first position neither relay 510 nor relay 520 operates so that neither the automatic nor the digital impulsing circuit is closed or prepared for units switch magnet 550.

Assuming that the special service-unit is idle, battery is connected to test conductor 583 which is a part of cable C5% and upon release of relay 450 at the end-of the digit the following circuit is closed for relays 480 and 746 in series: ground, contacts 414, 435 and 422; Fig. 4, lower winding of relay 480, contacts-485 and-451, conductor 465, contact 521, Fig. 5, C wiper 565 and first contact in the C bank of tens switch TS, conductor 583, contact 841, Fig. 8, conductor 737, contact 761, Fig. 7, winding of relay 740, battery. In operating, relay 480-at its preliminary contact 484 closes a locking circuit extending from ground at contact 414 to the upper winding of relay 480; at contacts 482 and 483, the relay closes ringing generator and ground to wipers 563 and 564 of the tens switch, respectively, but at the present instance the ringing circuit cannot be completed dueto the fact that contacts 1 in the line banks ofthe tens switch are unconnected; and at 481 the relay closes ring-back-tone to the calling line. This tone is immediately disconnected again when the finder-connector link releases as described below; in fact transmission of ring-back-tone to the calling party could be avoided in the present case if desired by taking the right-back-tone circuit through a break contact not shown on special service relay 350. At contact 486, relay 480 closes direct ground to C wiper 565 to insure'the operation of relay 740 and busy the special service calling number.

When relay 740 operates it closes at its contact 741, a pre-energizing circuit for finder test relay 7-30 and a circuit for relay 720 in parallel. The first of these circuits extends from ground through contacts 751 and 741, resistance 785 and the upper winding of relay 730 to battery but relay 730 cannot operate when thus energized over its upper winding with resistance 785 in series. The second of the aforementioned circuits may be traced from ground through contacts 751, 741, 731, 781 and the winding of relay 720 to battery. At its contact 742, relay 749 also closes a point in the testing circuit for relay 730, this circuit extending over the above mentioned EC conductor 189. Relay 720 in operating at its contact 721 causes the energization of finder magnet 780 so that this magnet in operating opens its interrupter contact 781, thereby opening the circuit of relay 720. Upon the release of this last mentioned relay the circuit of magnet 78d is interrupted at contact 721 and upon the release of magnet 78%) special finder CF advances its wipers from the position on which it happens to rest to the next following position.

The aforementioned interaction between relay 720 and magnet 780 repeats itself until finder CF has found the calling line. At this time the following test circuit is closed for relays 730 and 360 in series: ground, Winding of relay 36% Fig. 3, conductor 398, contact 424, conductor 392, contact 352, Fig. 3, conductor 328, contact 419A, Fig. 4, conductor 329, EC Wiper 384 and the first EC bank contact of line finder LF, condutor 189, first contact in the EC bank of finder CF, Fig. 7, EC wiper 728 of this last-mentioned switch, lower winding of relay 730, contacts 742 and 752, resistance 784, battery.

Test relay 730 upon operating in this circuit at its 

